1. Field of the Invention
The present invention relates to an apparatus for controlling cycles of optical pulse streams which are used for data reception and transmission in communication systems or the like. Particularly the present invention relates to an apparatus for controlling cycles of optical pulse streams based on a time correlation.
2. Description of the Prior Art
Recently, the researches on the processing of ultra-high optical signals for optical communications are briskly carried out. In connection to this, the all-optical circulating shift register and the clock frequency division are the important elements in the all-optical communication network.
The former is used as an optical block memory, i.e., as an optical buffer, while the latter can be used as a clock frequency division for inversely multiplexing the optical time division multiplex signals.
An all-optical circulating shift register which has an inverter and utilizes an optical multiplication logic and a nonlinear optical loop mirror (NOLM) based on a diffusion-shifted fiber (DSF) was first carried out in the following reference. [N. A. Whitaker, Jr., M. C. Gabriel, H. Avrampoulus, and A.
Huang, xe2x80x9cALL-OPTICAL, ALL-FIBER CIRCULATING SHIFT REGISTER WITH AN INVERTERxe2x80x9d, Opt. Lett., vol. 16, No. 24, pp 1999-2001, 1991].
This DSF-NOLM method is capable of realizing an ultrahigh speed operation, but its structure is bulky, and requires a high switching energy.
Recently, the ultra-high speed all-optical switching, the wavelength converter and the optical regenerator are briskly studied based on the non-linearity of a semiconductor optical amplifier. These devices are calling attention, because they have the possibility of a high operation speed. Particularly, they can be made into a compact form, and therefore, they are being illuminated as important components.
Further, an all-optical circulating shift register which utilizes the multiplication logic function using a time correlation device for setting a semiconductor optical amplifier in the optical fiber loop mirror was experimentally proved in the following reference [A. J. Poustie, R. J. Manning, and K. J. Blow, xe2x80x9cALL-OPTICAL CIRCULATING SHIFT REGISTER USING A SEMICONDUCTOR OPTICAL AMPLIFIER IN A FIBER LOOPxe2x80x9d, Electron. Lett., vol 32, pp 1215-1216, 1996]
Recently, a circulating shift register of 40 Gb/s using an interferometer based on a semiconductor optical amplifier was realized in the following reference [K. L. Hall, J. P. Donnelly, S. H. Groves, C. I. Fennely, R. J. Bailey, and A. Napoleowe, xe2x80x9c40 Gb/s ALL-OPTICAL CIRCULATING SHIFT REGISTER WITH AN INVERTERxe2x80x9d, Opt. Lett., vol. 22, pp 1479-1481, 1997].
Further, a clock frequency division for an input optical pulse stream of 10 GHz and 20 GHz was successfully carried out in the following reference. [A. E. Kelly, R. J. Manning, A. J. Poustie, and K. J. Blow, xe2x80x9cALL-OPTICAL CLOCK DIVISION AT 10 AND 20 GHz IN A SEMICONDUCTOR OPTICAL AMPLIFIER BASED ON NONLINEAR LOOP MIRRORxe2x80x9d, Electron. Lett., vol. 34, pp 1337-1339, 1998]
In the above described conventional methods, however, the feedback optical pulses are incident into the optical fiber loop perpendicularly to the input optical pulses, so that the feedback optical pulses can serve as switching optical pulses. Therefore, the total system essentially becomes sensitive to the polarized beams. Further, a switching technique based on the circulation of polarized beams is resorted to, and therefore, the system further becomes sensitive to the input polarized beams.
The present invention is intended to overcome the above described disadvantages of the conventional techniques.
Therefore it is an object of the present invention to provide an apparatus for controlling cycles of optical pulse streams, in which the feedback optical pulses and the input optical pulses are subjected to a time interleaving so as to make them not overlapped together, and then they are subjected to a time correlation, thereby considerably reducing the polarized beam dependence of the input optical pulse streams.
In achieving the above object, the apparatus for controlling cycles of optical pulse streams according to the present invention includes: a clock generating means for generating clocks; an optical pulse generating means for receiving the clocks from the clock generating means to generate optical pulses in synchronization with the clocks of the clock generating means; an input optical pulse distributing means for distributing feedback optical pulses of an output optical pulse distributing means, and for distributing the optical pulses of the optical pulse generating means; a time correlation means for correlating a time of optical pulses of the input optical pulse distributing means; an optical pulse transferring means for amplifying and filtering the optical pulses of the time correlation means, and for attenuating them before transferring them; and the output optical pulse distributing means distributing the optical pulses of the optical pulse transferring means to transfer them to an output terminal and to the input optical pulse distributing means.